This invention is concerned with electrostatic discharge protection for microwave structures and circuits, more particularly, with devices and methods that provide electrostatic discharge protection with minimal disruption and interference with the structure and operation of microwave guided wave structures.
Electrostatic discharge protection devices for electronic systems operating at frequencies below 1 GHz are well known. More recently, there has been a need for providing electrostatic discharge protection in higher frequency (microwave) structures and circuits that operate above 1 GHz (e.g., between 1 GHz and 20 GHz). Waveguide structures operating in the microwave regime include microstrip, stripline, and coplanar guide structures, for example. Prior protection devices, such as zener diodes and variable resistors, have a rather large capacitance that interferes with the desired operation of microwave structures and circuits. The large capacitance and the inductance of the packaging leads create a self resonance that limits the utility of such devices above 1 GHz. Moreover, the packaging and mounting of the prior art protection devices further limit their use.
Any electrostatic discharge device should provide minimum disruption or loading of the circuits with which they are used. Furthermore, when the voltage levels associated with the build up of electrostatic charges reach a threshold level, the devices should act quickly to present a low impedance path for electrostatic discharge. Once the voltage threshold is reached (typically 100-2000 volts), the electrostatic discharge should lower the voltage by a factor of 50% or more by rapidly and fully conducting excess charge to ground.
Prior to the present invention, there have been no effective and practical electrostatic discharge devices for use in microwave structures and circuits.